α-Lactalbumin: structure and function

Small milk protein α-lactalbumin (α-LA), a component of lactose synthase, is a simple model Ca 2+ binding protein, which does not belong to the EF-hand proteins, and a classical example of molten globule state. It has a strong Ca 2+ binding site, which binds Mg 2+, Mn 2+, Na +, and K +, and several distinct Zn 2+ binding sites. The binding of cations to the Ca 2+ site increases protein stability against action of heat and various denaturing agents, while the binding of Zn 2+ to the Ca 2+-loaded protein decreases its stability. Functioning of α-LA requires its interactions with membranes, proteins, peptides and low molecular weight substrates and products. It was shown that these interactions are modulated by the binding of metal cations. Recently it was found that some folding variants of α-LA demonstrate bactericidal activity and some of them cause apoptosis of tumor cells.